Folypolyglutamate synthetase (FPGS) catalyzes the addition of glutamic acid to folates and antifolates and as a result, causes the retention of these compounds in normal and neoplastic cells. The overall goals of this research are to understand the mechanism of the reaction catalyzed by the enzyme isolated from neoplastic tissue, to study the turnover of the enzyme in growing, static and differentiating tissues and to evaluate gene transfer methods for cloning the gene that codes for mammalian FPGS. The proposed work would (1) purify FPGS from rodent and human tumors, (2) kinetically characterize the sequence of addition of substrates to these enzymes, (3) study the time course of expression of enzyme activity in developing and differentiating tissues, (4) investigate the turnover of enzyme, and (5) attempt the isolation of a DNA clone that codes for human enzyme. These studies offer a better understanding of how FPGS works, when it is expressed and how its synthesis is controlled.